1. Field
The present application relates to a hybrid vehicle automatic simulated shifting, which simulates engine sounds at shift points anticipated by the driver.
2. Description of the Related Art
Hybrid vehicles have improved fuel economy over conventional automobiles through the efficient use of two or more power sources. Hybrid vehicles can utilize a power split architecture, which includes an engine and electric motor-generators having separate power paths to independently provide power to the wheels. However, a step transmission used in conventional automobiles is unsuitable for transmitting power from both the engine and the motor-generators to the wheels. Instead, hybrid vehicles can employ an electrically controlled variable transmission (ECVT).
Unlike a conventional step transmission, an ECVT does not select from fixed gear ratios, or gears. An ECVT utilizes a planetary gear, the motor-generators, and control circuitry to adjust the spin rate of the engine. This allows the ECVT to control the engine speed independently of the vehicle speed. The engine speed has no direct relation to the vehicle's acceleration or speed. However, drivers are accustomed to conventional step transmissions where the engine speed is linked to the gears.
With a step transmission, the engine speed increases as the vehicle accelerates. The increasing engine speed generates noise, which serves as an audible cue for drivers to shift gears. Drivers also associate the engine noise with power and performance. The acceleration is interrupted when shifting gears, which drivers are also accustomed to. Because an ECVT has no fixed gears, and further modulates the engine speed with the motor-generator output, hybrid vehicles do not produce the same engine flares while accelerating. The ECVT also provides for smooth acceleration, with no jerks related to shifting gears. Hybrid vehicles may feature a sequential gear logic, which provides simulated gears. Paddle shifters allow drivers to manually shift to the simulated gears. The sequential gear logic further provides automatic upshifting. However, the sequential gear logic does not provide for automatic downshifting. Drivers seeking a sporty driving experience lose the engine sounds associated with downshifting a conventional step transmission.
Thus, there is a need for a hybrid vehicle which enhances driver experience by automatically simulating downshifts as anticipated by the driver.